1. Field of the Invention
The present invention relates to a touch panel for a display device which is disposed close to a display surface of a display device such as a liquid crystal display device and generates a specified signal corresponding to a position touched when an operator touches a desired position on a panel surface with a pen or a finger based on information displayed on the display surface.
2. Description of the Related Art
Since the panel surface of this type of a touch panel can be used for both display and input of information, the utilization factor of the panel surface is increased, and the touch panel is in demand for compact information processors and communication equipment, in particular, mobile communications terminals.
FIG. 2 is a sectional view of a conventional touch panel (disclosed in FIG. 2 in Japanese Unexamined Patent Application Publication No. 2000-187197).
As shown in FIG. 2, a touch panel 10 basically comprises a pair of resistive layers (fist and second resistive layers) 12 and 13 disposed opposite to each other across a plurality of insulating dot spacers 11, and a flat transparent plate protecting the second resistive layer, for example, a transparent glass plate 16. The second resistive layer 13 is laid on the glass plate 16 while the touch panel 10 is disposed close to the display device 30 such that the glass plate 16 faces the display surface of the display device 30.
In this construction, when an outer surface of the first resistive layer 12 is touched to be pressed, a touched portion of the first resistive layer 12 is brought into contact with a portion opposite thereto of the second resistive layer 13, and a signal corresponding to the contact position (touched position) is generated.
In a practical construction, a transparent layer, for example, a Polyethylene Terephthalate film (hereinafter, referred to as xe2x80x9cPETxe2x80x9d 15, is laminated on an outer surface of the first resistive layer 12 for protecting thereof, so the touching operation is implemented on this PET film 15.
The first and second resistive layers 12 and 13 are combined at their peripheries by means of a sealing member 14 thereby making them dustproof and waterproof.
A light unit is added to the above-described display device 30 to illuminate the display surface brightly for making it easy to observe. A front light unit 20 to shine light on a front face (display surface) of the display device 30 is often used as the light unit in recent years.
FIG. 2 shows the touch panel 10 attached to the display device 30 having the front light unit 20 above described.
As shown in FIG. 2, the front light unit 20 has a light conductive plate 22 disposed facing the display surface of the display device 30, and guides light emitted from a light source 21 located along the light source 21 toward the display surface of the display device 30 through the light conductive plate 22. The light made incident on the display surface enters the display device 30, is reflected at a bottom surface thereof, travels through the light conductive plate 22 and the touch panel 10, and exits out (refer to an arrow indicated by a broken line in the figure), whereby an image on the display surface is visualized.
An array of prisms whose respective ridges are parallel to each other are formed on a surface opposite to a surface facing the display surface of the display device 30 so that, as described above, the light conductive plate 22 can guide light coming therein from its end toward the display surface of the display device 30 disposed therebelow.
However, in the conventional technology shown in FIG. 2, since the touch panel 10 and the front light unit 20 are constituted independent of each other, the touch panel 10 is easily subjected to the vibration and shock. And, because the touch panel 10 is required for strength against the vibration and shock when mounted on the device body, the thickness of the glass plate 16 needs to be increased so as to avoid damages on the glass plate 16. However, there is a problem that the whole thickness (the depth) D of the display device 30 is increased when attached to the touch panel 10. There is another problem that since the light conductive plate 22 is brought into a direct contact with the glass plate 16, the light conductive plate 22 can be damaged or broken by the glass plate 16 when a vibration or shock is applied to the touch panel 10.
Thus, a touch panel for a display device (the touch panel shown in FIG. 1 in the above-described Japanese Unexamined Patent Application Publication) was disclosed, where, as shown in FIG. 3, a second resistive layer 13 of a touch panel 10 is in a close contact with a surface of a light conductive plate 22, on which an array of prisms are formed.
In this touch panel, a member (the glass plate 16 in FIG. 2) interposed between the light conductive plate 22 and the second resistive layer 13 of the touch panel 10 is eliminated, and the touch panel 10 is integrated with a front light unit 20, and thus, the whole thickness D can be reduced when the touch panel and the front light unit are attached to a display device 30. Further, the glass plate 16 in FIG. 2 is not present, and thereby the problem that the light conductive plate 22 is damaged or broken by the glass plate when a vibration or shock is applied to the touch panel 10 can be solved.
However, there is a problem described below in the conventional technology shown in FIG. 3.
Since the second resistive layer 13 is in a close contact with the surface of the light conductive plate 22, on which the array of prisms are formed, as described above, a surface facing a first resistive layer 12 is also uneven corresponding to the surface of the array of prisms, and insulating dot spacers 11 are interposed between the uneven surface of the second resistive layer 13 and a flat surface of the first resistive layer 12.
Thus, the linearity of the resistance value at each position on a touch panel operation surface (surface of the PET film 15) is difficult to ensure, and errors occur easily in information obtained on the position.
In addition, there is a durability problem that projecting portions of the prisms formed on the one surface of the light conductive plate 22 and projecting portions of the second resistive layer 13 to cover the light conductive plate are easily damaged while the touch panel 10 is used.
Accordingly, it is an object of the present invention to provide a touch panel for a display device, which combines advantages of the conventional technologies shown in FIGS. 2 and 3 that the whole thickness is not increased excessively when the touch panel is attached to the display device, the light conductive plate is not damaged or broken when a vibration or shock is applied to the touch panel, no errors occur in information obtained on the position, the touch panel operation surface does not become wavy, the display quality is not degraded, and that the durability is excellent.
According to the present invention, in a touch panel for a display device which is structured such that one resistive layer of a pair of resistive layers disposed facing each other across a plurality of insulating dot spacers is laid on a translucent flat plate, is disposed close to a display device such that the translucent flat plate is directed toward a display surface of the display device and that a front light unit comprising a light source and a light conductive plate to guide light emitted from the light source toward the display surface of the display device is interposed therebetween, and in which a signal is generated by touching an outer surface of the other resistive layer corresponding to a position touched, wherein the translucent flat plate is formed of a polyethylene terephthalate film, and the light conductive plate is integrally combined with an outer surface of the polyethylene terephthalate film.